Conventionally, as an apparatus for judging the state of an assembled battery of this kind, the following apparatus has been proposed. That is, a voltmeter is attached to each of a plurality of battery blocks composed of one or a plurality of single cells constituting an assembled battery for supplying power to a load. The voltmeter is used for measuring the voltage of each of the plural battery blocks simultaneously. Then, the apparatus judges an abnormality of the assembled battery on the basis of the respective voltages measured simultaneously. When a deviation of two voltages among the respective voltages measured simultaneously is equal to a predetermined value or more, the apparatus considers that there is an overdischarged single cell, and judges the assembled battery to be abnormal.
However, the apparatus for judging the state of an assembled battery of this type has the possibility of misjudgment of an abnormality of the assembled battery when each voltage of a plurality of battery blocks cannot be simultaneously measured. That is, because the single cells of the battery blocks include internal resistance, there may be cases where a deviation of voltages equal to the predetermined value or more is produced though the assembled battery when the current flowing the assembled battery changes in a process of measuring each voltage of the plural battery cells, and this in fact normal. The possibility of the misjudgment is based on the above matter. Such a problem is highlighted in the system in which the current flowing an assembled battery greatly changes.
An apparatus for judging the state of an assembled battery of the present invention has an advantage of solving such a problem and to perform the accurate judgment of the state of a battery by the use of an apparatus which cannot simultaneously detect each voltage of a plurality of battery blocks. Moreover, the apparatus for judging the state of an assembled battery of the present invention has another advantage of performing the accurate judgment of the state of a battery by the use of a more inexpensive apparatus.